Polyurethane coatings are commonly used over functional and/or decorative floor coatings or as sealers for concrete, wood, metal, plastic, and the like. Such polyurethane coatings are often formulated as organic solvent-based systems because of factors such as, for example, the hydrophobicity and viscosity of polyurethane resins.
Interest in the use of water as an alternative carrier for polyurethane coatings has increased due to health, safety, and environmental concerns over the effects of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). As a result, waterborne polyurethane coating technologies have emerged as alternatives to solventborne coating technologies. Two-component waterborne polyurethane coating systems represent one such alternative to solventborne coating technologies.
Two-component waterborne polyurethane coating systems generally include a water-dispersible polyisocyanate component and a water-dispersible polyol or polyamine component. The two components are mixed to form an aqueous dispersion and applied to a substrate where the water evaporates and the isocyanate groups of the polyisocyanate component react with the hydroxyl groups or amine groups of the polyol or polyamine component to form a urethane- or urea-crosslinked coating. Two-component waterborne polyurethane coatings may exhibit many properties that are comparable to solventborne polyurethane coatings including, for example, abrasion resistance, chemical resistance, hardness, gloss, and the like. However, two-component waterborne polyurethane coatings may possess disadvantages relative to solventborne coating systems.
The physical drying rate and the chemical curing rate of two-component waterborne polyurethane coatings may be one such disadvantage. Two-component waterborne polyurethane coatings may physically dry and chemically cure at a slower rate than solventborne coating systems. This may be problematic for coating applications that require or would otherwise benefit from increased drying and curing rates and a rapid return to service of coated substrates. For example, coatings for flooring or other high traffic substrates may benefit from increased drying and curing rates and a rapid return to service when coated with waterborne polyurethane coatings.